1. Field
This specification relates to a system for performing phase-sensitive regeneration without a phase-locked loop.
2. Description of the Related Art
All-optical regeneration of phase-shift-keyed (PSK) data channels reduce phase noise and increase communication system performance. Phase-dependent data modulation formats for optical communication systems provide tolerance to nonlinear effects and spectral efficiency. Phase-modulated data channels may benefit from optical regeneration to avoid full optical-electrical-optical conversion in long distance systems. Phase-sensitive amplification (PSA) may be used to attenuate or squeeze the phase noise. Two pumps and a data channel mix with each other, but this mixing is efficient only when the pumps and the data channel have the same phase and are coherent with each other. The part of the signal that is a different phase from the pumps, such as the phase noise, will be “squeezed” or attenuated. Various approaches for phase-locking the pumps and the data channel include: (i) using a phase-locked loop (PLL) to adjust the relative phase alignment, and (ii) using a comb of mutually coherent frequency lines as well as cross-phase modulation between one of the comb lines and the data channel.
Accordingly, there is a need for a system and method to phase-lock the signal without a PLL.